I have Lumia 730(windows 8.1) phone. I just went through some apps and want to clear cache memory of some apps. How can I clear app data, cache?
Unfortunately , WP doesn't allow us to remove App Cache globally. It is totally dependent on Developer to add such functionality for his app. The only possible way to delete the cache is to delete the app and install it again.
You can find more here
If you are worried about WhatsApp means then you have to delete the chat history and also to delete media of all groups. Which will release some app data for whatsapp.